The present application claims priority to Japanese Patent Application No. 11-90914 filed Mar. 31, 1999, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an adjusting device for use in an image reading apparatus, and more particularly to an adjusting device used in an image reading apparatus for adjusting the state of focus and the optical magnification factor in an imaging section of the image reading apparatus.
2. Description of the Related Art
It has been known heretofore to provide an image reading apparatus which scans a reading target by illuminating it with light and which reads the reflected light as image information. A device for detecting the state of focus in an imaging section of such an image reading apparatus is disclosed, for example, in Japanese Unexamined Patent Publication No. 5-276331. This device detects the state of focus by reading a ladder chart by means of a reader.
In an image reading apparatus, an automatic document feeder is used to sequentially read a plurality of documents. During such sequential document reading, the temperature inside the apparatus rises and the refractive index of a lens or the like in an optical system changes, causing focus and magnification errors. The prior art, however, has had the problem that, to detect such focus or magnification errors, the sequential document reading operation must be stopped temporarily and the reading of the chart, etc. must be performed once again.
An object of the present invention is to solve the above problem.
A further object of the present invention is to provide an adjusting device for use in an image reading apparatus that can easily adjust the state of focus and the optical magnification factor.
These and other objects are achieved by an image reading apparatus, comprising: an image sensor; an optical system for exposing a reading target to light, and for projecting image light of the reading target onto an image sensor; a temperature sensor for measuring temperature inside the apparatus; an adjusting mechanism for adjusting at least either a state of focus or a reading magnification factor on the image sensor; and a control circuit for controlling the adjusting mechanism to make the adjustment based on the temperature measured by the temperature sensor.
In this image reading apparatus, since at least either the state of focus or the reading magnification factor is adjusted based on the measured temperature, the adjustment can be made easily.
Preferably, a detection means is provided for detecting at least either the state of focus or the reading magnification factor on the image sensor by using a chart, wherein during sequential reading of reading targets, the adjustment is made using the adjusting mechanism, and at other times, the adjustment is made based on the result of the detection from the detection means.
According to the present invention, since, during the sequential reading of the reading targets, the adjustment is made based on the measured temperature, it becomes possible to provide an image reading apparatus that allows the adjustment to be made without having to interrupt the reading operation in progress.
Preferably, the adjusting mechanism moves the image sensor or part of the optical system. Also preferably, the adjusting mechanism makes the adjustment based on the temperature at the time that the image sensor starts reading and on the measured temperature.
It is preferable that the temperature sensor is provided in close proximity to an optical element having the highest refractive power in the optical system. When the temperature sensor is thus provided in close proximity to the optical element having the highest refractive index in the scanning optical system, the adjustment can be made with higher accuracy.